With the miniaturization of semiconductor integrated circuit devices, for example, in order to reduce parasitic capacitance between gates of transistors, there is a need for a low-k spacer formed by a low-k film having a lower dielectric constant than SiO2. Examples of films used for the low-k spacer may include a silicon oxycarbonitride (SiOCN) film and a silicon oxycarbide (SiOC) film. There have been proposed conventional methods for forming the SiOCN film or the SiOC film using a CVD method or an ALD method.
In the proposed methods, when the SiOCN film or the SiOC film is formed using the CVD method or the ALD method, a silicon film containing carbon and nitrogen is first formed and the SiOCN film or the SiOC film is then formed by oxidizing the carbon and nitrogen-containing silicon film. Reactants (oxygen-containing active species) such as O2, O3, N2O, O2 plasma, O radicals and so on are used for this oxidation.
However, the oxidizing power of such reactants (oxygen-containing active species) used for the oxidation is too strong. As a result, it may oxidize bonds such as Si—C, Si—N and so on. This makes it difficult to form an SiOCN film having a high concentration of carbon and nitrogen and an SiOC film having a high concentration of carbon.
For example, the percentages of carbon and nitrogen contained in a SiOCN film formed using the oxygen-containing active species result in low levels of both, e.g., below 10%. Similarly, the percentage of carbon contained in the SiOC film formed using these oxygen-containing active species is also low, e.g., below 10%.